1. Field of the Invention
The present invention relates to liquid crystal display devices. More particularly, the present invention relates to in-plane switching mode liquid crystal display devices that provide high-image quality and high-aperture ratio, and a fabricating method thereof.
2. Discussion of the Related Art
In general, a liquid crystal display (LCD) device uses the optical anisotropy and polarization properties of liquid crystal molecules. Liquid crystal molecules have a definite orientational alignment resulting from their thin and long shape. The alignment direction of the liquid crystal molecules can be controlled by application of an electric field to the liquid crystal molecules. Accordingly, as an intensity of the applied electric field changes, the alignment orientation of the liquid crystal molecules also changes. Because incident light through a liquid crystal material is refracted based upon an orientation of the liquid crystal molecules resulting from the optical anisotropy of the aligned liquid crystal molecules, an intensity of the incident light can be controlled and images can be displayed.
Among the various types of LCD devices commonly used, active matrix LCD (AM-LCD) devices, in which thin film transistors (TFTs) and pixel electrodes connected to the TFTs are disposed in a matrix, have been developed because of their high resolution and superior display of moving images.
The LCD device includes upper and lower substrates, and a liquid crystal layer interposed therebetween. The upper substrate, which is referred to as a color filter substrate, has a common electrode and the lower substrate, which is referred to as an array substrate, has a pixel electrode. The liquid crystal layer is driven by an electric field generated between the common electrode and the pixel electrode. The LCD device having the common electrode and the pixel electrode on opposite substrates has excellent transmittance and aperture ratio. However, because the electric field is generated perpendicular to the upper and lower substrates, the LCD device has a poor viewing angle property. To solve the problem of narrow viewing angle, new LCD devices such as an in-plane switching (IPS) mode LCD device, where an electric field is laterally generated, may be used.
FIG. 1 is a schematic cross-sectional view of an in-plane switching mode liquid crystal display device according to the related art.
In FIG. 1, an upper substrate 10 and a lower substrate 20 face to and are spaced apart from each other. A liquid crystal layer 12 is interposed between the upper and lower substrates 10 and 20. A pixel electrode 36 and a common electrode 38 are formed on an inner surface of the lower substrate 20. The liquid crystal layer 12 is driven with a horizontal electric field generated between the pixel electrode 36 and the common electrode 38.
Because the liquid crystal molecules are re-aligned along a horizontal electric field, the IPS mode LCD device has a wide viewing angle. For example, users can see images having a respective viewing angle of about 80° to about 85° along top, bottom, right and left directions with respect to a normal direction of the IPS mode LCD device.
FIGS. 2A, 2B and 3 are schematic views showing an in-plane switching mode liquid crystal display device according to the related art. FIG. 2A is a plan view showing an array substrate, and FIG. 2B is a plan view showing a color filter substrate. FIG. 3 is a cross-sectional view taken along a line “III—III” of FIGS. 2A and 2B showing the in-plane switching mode liquid crystal display device including a liquid crystal layer therein.
In FIG. 2A, a gate line 42 is formed in a first direction on a first substrate 40, and a data line 58 crosses the gate line 42 in a second direction to define a pixel region “P.” A thin film transistor “T” is connected to the gate line 42 and the data line 58.
Additionally, a common line 46 is substantially parallel to and spaced apart from the gate line 42. An auxiliary common line 69 is connected to the common line 46 thereon and a plurality of common electrodes 70 extend from the auxiliary common line 69 in the second direction and are located in the pixel region “P.”
The pixel line 66 is connected to the thin film transistor “T,” a plurality of pixel electrodes 68 extend from the pixel line 66 in the second direction and are located in the pixel region “P.” Moreover, each of the common electrodes 70 and each of the pixel electrodes 68 are formed in an alternating pattern.
The pixel line 66, the auxiliary common line 69, the pixel electrode 68, and the common electrode 70 are made of the same material. The material may be, for example, transparent conductive materials.
In FIG. 2B, a black matrix 82 is formed on a second substrate 80 at a boundary of the pixel region “P” shown in FIG. 2A and includes an open portion 81 corresponding to the pixel region “P” (of FIG. 2A).
In addition, a color filter layer 84 is formed in the open portion 81 of the black matrix 82 over the second substrate 80. The color filter layer 84 may include red, green and blue color filters 84a, 84b and 84c, in which each of the red, green and blue color filters 84a, 84b and 84c are located in a corresponding position with reference to the pixel region “P.” An overcoat layer 86 is formed on an entire surface of the color filter layer 84 and the black matrix 82 to make the surface of the color filter layer 84 flat. Because the second substrate 80 having a color filter layer 84 in the in-plane switching mode liquid crystal display devices does not include any electrode pattern, the overcoat layer 86 for flattening the surface may be desired on the color filter layer 84.
In FIG. 3, a gate electrode 44 and a common line 46 are formed on a first substrate 40. A gate insulating layer 48 is formed on an entire surface of the gate electrode 44 and the common line 46 over the first substrate 40, and a semiconductive layer 50 is formed on the gate insulating layer 48 over the gate electrode 44.
Additionally, a source electrode 54 and a drain electrode 56 are formed on the semiconductive layer 50, and a data line 58 is formed as one body with the source electrode 54. Moreover, a semiconductive material layer 52 is correspondingly formed with the source electrode 54, the drain electrode 56 and the data line 58 therebelow and is one body with the semiconductive layer 50.
The gate electrode 44, the semiconductive layer 50, the source electrode 54 and the drain electrode 56 form a thin film transistor “T.”
A passivation layer 64 is formed over an entire surface of the first substrate 40 including the thin film transistor “T” and includes a drain contact hole 60 that exposes a portion of the drain electrode 56 and a common line contact hole 62 that exposes a portion of the common line 46. The common line contact hole 62 passes through the gate insulating layer 48 and the passivation layer 64 to expose the portion of the common line 46.
A pixel line 66 is formed on the passivation layer 64 and is connected to the drain electrode 56 via the drain contact hole 60. A plurality of pixel electrodes 68 extend from the pixel line 66 and are located in the pixel region “P.”
In addition, an auxiliary common line 69 is formed on the passivation layer 64 and is connected to the common line 46 via the common line contact hole 62. Although not shown in FIG. 3, a plurality of common electrodes 70 extend from the auxiliary common line 69 and are located in the pixel region “P.” Each of the common electrodes 70 and each of the pixel electrodes 68 are formed in an alternating pattern.
A black matrix 82 is formed on an inner surface of the second substrate 80 shown in FIG. 2B. The black matrix 82 includes the open portion 81 shown in FIG. 2B corresponding to the pixel region “P” (of FIG. 2A). A color filter layer 84 is formed in the open portion 81 of the black matrix 82 over the second substrate 80. The color filter layer 84 includes red, green and blue color filters 84a, 84b and 84c, and each of the red, green and blue color filters 84a, 84b and 84c are located in a corresponding portion of the pixel region “P.” An overcoat layer 86 is formed on an entire surface of the color filter layer 84 and the black matrix 82.
A liquid crystal layer 90 is interposed between the first and second substrates 40 and 80 and includes liquid crystal molecules 89 that are driven by a horizontal electric field 88 generated between the pixel electrode 68 and the common electrode 70.
Although not shown in FIG. 3, first and second alignment layers are formed on both surfaces of the first and second substrates 40 and 80 directly contacting the liquid crystal layer 90, respectively.
In the related art, undesired light in the non-pixel region at the boundary of the pixel region is shielded by the black matrix. Accordingly, because the black matrix should be located to correspond with the non-pixel region of the facing substrate to prevent undesired light in the non-pixel region, a line width of the black matrix increases based upon the alignment margin. The alignment margin of the black matrix effects the misalignment of the two substrates that face each other. Therefore, the aperture ratio of the in-plane switching mode liquid crystal display device of the related art decreases.
If the alignment margin value is too small, image quality damage such as contrast ratio and cross talk may be caused by the light leakage phenomenon in the non-pixel region.